In addressing the use of noble metal-dressed carbon nanotubes (CNTs) as a substrate for surface enhanced Raman scattering (SERS) we re-direct attention from interactions at the outer interface with deposited molecular species to interactions at the inner (silver-CNT) interface and the extraction of enhanced D- and G-band signals from the CNTs themselves. This offers a means for reliable, Raman-based characterization of vertically aligned CNTs at a sensitivity improved by over an order magnitude; obtaining data from individual CNTs is readily achievable. Experimental data will be interpreted with the assistance of electromagnetic modelling of the optical response.
Over the last few years a number of sensing platforms are being investigated for their use in drug development, microanalysis or medical diagnosis. Lab-on-a-chip (LOC) are devices integrating more than one laboratory functions on a single device chip of a very small size, and typically consist of two main components: microfluidic handling systems and sensors. The physical mechanisms that are generally used for microfluidics and sensors are different, hence making the integration of these components difficult and costly. In this work we present a lab-on-a-chip system based on surface acoustic waves (for fluid manipulation) and film bulk acoustic resonators (for sensing). Coupling surface acoustic waves into liquids induces acoustic streaming and motion of micro-droplets, whilst it is well-known that bulk acoustic waves can be used to fabricate microgravimetric sensors. Both technologies offer exceptional sensitivity and can be fabricated from piezoelectric thin films deposited on Si substrates, reducing the fabrication time/cost of the LOC devices.
Here we present our on-going efforts toward the development of stable ballasted carbon nanotube-based field emitters
employing hydrothermally synthesized zinc oxide nanowires and thin film silicon-on-insulator substrates. The
semiconducting channel in each controllably limits the emission current thereby preventing detrimental burn-out of
individual emitters that occurs due to unavoidable statistical variability in emitter characteristics, particularly in their
length. Fabrication details and emitter characterization are discussed in addition to their field emission performance. The
development of a beam steerable triode electron emitter formed from hexagonal carbon nanotube arrays with central
focusing nanotube electrodes, is also described. Numerical ab-initio simulations are presented to account for the
empirical emission characteristics. Our engineered ballasted emitters have shown some of the lowest reported lifetime
variations (< 0.7%) with on-times of < 1 ms, making them ideally-suited for next-generation displays, environmental
lighting and portable x-rays sources.
The promising field emission properties of carbon nanotubes, or CNTs, have resulted in them being identified as desirable sources for electron microscopes and other electron beam equipment. A new process to grow single CNTs aligned to the electron-optical axis inside electron source modules has been developed. The process involves putting the entire source-suppressor module inside a plasma-enhanced chemical vapour deposition reaction chamber. This is a process which can be scaled up to mass production. The resultant CNT electron sources were inserted into an electron microscope for imaging. Though current stability was found to be comparable to the tungsten cold-field emitter (with a maximum-minimum variation of 3-7% of the mean current over one hour), the reduced brightness was found to be an order of magnitude greater than a typical Schottky source (at 3×109 Acm2sr-1) with a kinetic energy spread of 0.28 eV. Imaging with a CNT source has produced a marked improvement in resolution when compared to a Schottky source using the same electron-optics. The properties measured show that the CNT source compares favourably with and in some cases improves upon other sources available today. In particular, the CNT source would be of most benefit to low-voltage, high-resolution microscopy.
We present a new photonic micro-optical device based on an array of electrodes made from vertically aligned multiwall
carbon nanotubes used to address a liquid crystal cell. The electrodes create a Gaussian electric field profile which is used
to reorient a planar aligned nematic liquid crystal. The variation in refractive index within the liquid crystal layer acts like
a graded index optical element which can be varied by changing the applied electric field to the carbon nanotube. Results
are presented from a device fabricated with a 10um pitch between the micro-optical elements.
Zinc oxide nanowire networks are attractive as alternatives to organic and amorphous semiconductors due to their wide bandgap, flexibility and transparency. We demonstrate the fabrication of thin film transistors (TFT)s which utilize ZnO nanowires as the semiconducting channel. These thin film transistors can be transparent and flexible and processed at low temperatures on to a variety of substrates. The nanowire networks are created using a simple contact transfer method that is easily scalable. Apparent nanowire network mobility values can be as high as 3.8 cm2/Vs (effective thin film mobility: 0.03 cm2/Vs) in devices with 20μm channel lengths and ON/OFF ratios of up to 104.
We present a new photonic micro-optical device based on an array of electrodes made from vertically aligned multiwall
carbon nanotubes used to address a liquid crystal cell. The electrodes create a Gaussian electric field profile which is used
to reorient a planar aligned nematic liquid crystal. The variation in refractive index within the liquid crystal layer acts like
a graded index optical element which can be varied by changing the applied electric field to the carbon nanotube. Results
are presented from a device fabricated with a 10um pitch between the micro-optical elements.
We present a new photonic micro-optical device based on an array of electrodes made from vertically aligned multiwall
carbon nanotubes used to address a liquid crystal cell. The electrodes create a Gaussian electric field profile which is used
to reorient a planar aligned nematic liquid crystal. The variation in refractive index within the liquid crystal layer acts like
a graded index optical element which can be varied by changing the applied electric field to the carbon nanotube. Results
are presented from a device fabricated with a 10μm pitch between the micro-optical elements.
Metal based thermal microactuators normally have lower operation temperatures than those of Si-based ones; hence they have great potential for applications. However, metal-based thermal actuators easily suffer from degradation such as plastic deformation. In this study, planar thermal actuators were made by a single mask
process using electroplated nickel as the active material, and their thermal degradation has been studied. Electrical tests show that the Ni-based thermal actuators deliver a maximum displacement of ~20 m at an average temperature of ~420 °C, much lower than that of Si-based microactuators. However, the displacement strongly depends on the frequency and peak voltage of the pulse applied. Back bending was clearly observed at a maximum temperature as low as 240 °C. Both forward and backward displacements increase with increasing the
temperature up to ~450 °C, and then decreases with power. Scanning electron microscopy observation clearly showed that Ni structure deforms and reflows at power above 50mW. The compressive stress is believed to be responsible for Ni piling-up (creep), while the tensile stress upon removing the pulse current is responsible for
necking at the hottest section of the device. Energy dispersive X-ray diffraction analysis revealed severe oxidation of the Ni-structure induced by Joule-heating of the current.
The maintenance of the growth of the multibillion-dollar semiconductor industry requires the development of techniques
for the fabrication and characterisation of nanoscale devices. Consequently, there is great interest in photolithography
techniques such as extreme UV and x-ray. Both of these techniques are extremely expensive and technologically very
demanding. In this paper we describe research on the feasibility of exploiting x-ray propagation within carbon nanotubes
(CNT's) for the fabrication and characterisation of nanoscale devices. This work discusses the parameters determining
the design space available. To demonstrate experimentally the feasibility of x-ray propagation, arrays of carbon
nanotubes have been grown on silicon membranes. The latter are required to provide structural support for the CNT's
while minimising energy loss. To form a waveguide metal is deposited between the nanotubes to block x-ray
transmission in this region at the same time as cladding the CNT's. The major challenge has been to fill the spaces
between the CNT's with material of sufficient thickness to block x-ray transmission while maintaining the structural
integrity of the CNT's. Various techniques have been employed to fill the gaps between the nanotubes including
electroplating, sputtering and evaporation. This work highlights challenges encountered in optimising the process.
A TiNi/diamond-like-carbon (DLC) microcage for biological application has been designed, fabricated and
characterized. A compressively stressed DLC film with TiNi pattern on top lifts the fingers upwards once they are
released from the substrate, and the microcage can be closed through shape memory effect of top TiNi film with
temperature below 80°C. Further heating above 100°C, the gradual opening of the microcage can be obtained due to
thermal bimorph effect. The biocompatibility of both the TiNi and DLC films has been proved using a cell-culture
method.
A number of in-plane spring-like micro-electro-thermal-actuators with large displacements were proposed. The devices take the advantage of the large difference in the thermal expansion coefficients between the conductive arms and the insulator clamping beams. The constraint beams in one type (the spring) of these devices are horizontally positioned to restrict the expansion of the active arms in the x-direction, and to produce a displacement in the y-direction only. In other two types of actuators (the deflector and the contractor), the constraint beams are positioned parallel to the active arms. When the constraint beams are on the inside of the active arms, the actuator produces an outward deflection in the y-direction. When they are on the outside of the active arms, the actuator produces an inward contraction. Analytical model and finite element analysis were used to simulate the performances. It showed that at a constant temperature, analytical model is sufficient to predict the displacement of these devices. The displacements are all proportional to the temperature and the number of the chevron sections. A two-mask process is under development to fabricate these devices, using Si3N4 as the insulator beams, and electroplated Ni as the conductive beams.
Three types of micropumps based on TiNi shape memory alloy thin films were designed and fabricated. The TiNi films were prepared on silicon substrate by co-sputtering TiNi target and a separate Ti target at room temperature, and then post annealed at 650°C. The first pump design is based on a single TiNi/Si bimorph membrane structure with inlet and outlet. The second design is based on three layer structures bonded together, with one TiNi/Si active membrane structure and two layers of check valves. The third design is based on two TiNi/SU-8 composite structures, with TiNi as an actuation element, and SU-8/Si as a spring-back structure. The three types of micropump structures were fabricated based on the conventional MEMS processes.
The in-plane motion of microelectrothermal actuator ("heatuator") has been analyzed for Si-based and metallic devices. It was found that the lateral deflection of a heatuator made of a Ni metal is about ~60% larger than that of a Si-based actuator under the same power consumption. Metals are much better for thermal actuators as they provide a relatively large deflection and large force, for a low operating temperature and power consumption. Electroplated Ni films were used to fabricate heatuators. The electrical and mechanical properties of electroplated Ni thin films have been investigated as a function of temperature and plating current density, and the process conditions have been optimized to obtain stress-free films suitable for microelectromechanical systems applications. Lateral thermal actuators have been successfully fabricated, and electrically tested. Microswitches and microtweezers utilizing the heatuator have also been fabricated and tested.
William Milne, Ken Teo, N. Rupesinghe, L. Gangloff, E. Minoux, J.-P. Schnell, Dominique Dieumegard, F. Peauger, Pierre Legagneux, David Hasko, Gehan Amaratunga, Didier Pribat
Carbon nano-tubes are alternatives to conventional metal/silicon tips for field emission sources. They exhibit extraordinary field emission properties because of their high electrical conductivity, their high aspect ratio "whisker-like" shape for optimum geometrical field enhancement, and remarkable thermal stability. This paper will review the PECVD growth process, and the micro-fabrication techniques needed to produce well defined carbon nano-tube based micro-electron sources for use in a variety of applications.
TiNi films were deposited on silicon by co-sputtering TiNi target and a separate Ti target at a temperature of 450°C. Results from differential scanning calorimeter, in-situ X-ray diffraction and curvature measurement revealed clearly martensitic transformation upon heating and cooling. Two types of TiNi/Si optical micromirror structures with a Si mirror cap (20 micron thick) and TiNi/Si actuation beams were designed and fabricated. For the first design, three elbow shaped Si beams with TiNi electrodes were used as the arms to actuate the mirror. In the second design, a V-shaped cantilever based on TiNi/Si bimorph beams was used as the actuation mechanism for micromirror. TiNi electrodes were patterned and wet-etched in a solutions of HF:HNO3:H2O (1:1:20) with an etch rate of 0.6 μm/min. The TiNi/Si microbeams were flat at room temperature, and bent up with applying voltage in TiNi electrodes (due to phase transformation and shape memory effect), thus causing the changes in angles of micromirror.
Wireless capsule endoscopy (WCE) is a new technology to evaluate the patient with obscure gastrointestinal bleeding. However, there is still some deficiency existing in the current WCE, for example, lack of ability to biopsy and precisely locate the pathology. This study aimed to prepare and characterize TiNiCu shape memory alloy thin films for developing microgripper for biopsy (tissue sampling and tagging) applications. Ti50Ni41Cu9 thin films were prepared by co-sputtering of TiNi and Cu targets, and their transformation temperatures were slightly above that of human body. Results from differential scanning calorimetry, in-situ X-ray diffraction, curvature and electrical resistance measurement revealed clearly martensitic transformation of the deposited TiNiCu films upon heating and cooling. The biocompatibility of the TiNiCu films in the simulated gastric and intestinal solutions was also studied. Results showed the release of Ni and Cu ions is much less than the toxic level and the film did not lose shape memory effect even after 10-day immersion in the simulated solutions. TiNiCu/Si micro-cantilevers with and without electrodes were fabricated using the conventional micromachining methods and apparent shape memory effect upon heating and cooling was demonstrated.
The in-plane motion of microelectrothermal actuator ("heatuator") has been analysed for Si-based and metallic devices. It was found that the lateral deflection of a heatuator made of a Ni-metal is about ~60% larger than that of a Si-based actuator under the same power consumption. Metals are much better for thermal actuators as they
provide a relatively large deflection and large force, for a low operating temperature, and power consumption. Electroplated Ni films were used to fabricate heatuators. The electrical and mechanical properties of electroplated Ni thin films have been investigated as a function of temperature and plating current density, and the process
conditions have been optimised to obtain stress-free films suitable for MEMS applications. Lateral thermal actuators have been successfully fabricated, and electrically tested. Microswitches and microtweezers utilising the heatuator have also been fabricated and tested.
Microarraying involves laying down genetic elements onto a solid substrate for DNA analysis on a massively parallel scale. Microarrays are prepared using a pin-based robotic platform to transfer liquid samples from microtitre plates to an array pattern of dots of different liquids on the surface of glass slides where they dry to form spots diameter < 200 micrometers . This paper presents the design, materials selection, micromachining technology and performance of reservoir pins for microarraying.
We report here on properties of Metal-Semiconductor-Metal cells based on poly(3-octylthiophene), P3OT. The diodes were fabricated by spin-coating of poly (3-octylthiophene) on an indium-tin oxide coated glass substrate and an aluminum top contact was evaporated onto the film. The optical and electrical characteristics of the diodes were studied. A power efficiency of 10-4 was obtained at AM 1.5 conditions, while the power efficiency reached its maximum of 6% under illumination at 256 nm at an intensity of 2 (mu) W/cm2.
Gas sensors fabricated using conventional silicon microtechnology can suffer from a number of significant disadvantages when compared with commercially available thick-film, screen-printed devices. For example, platinum gate MOSFET devices normally operate only at a temperature of up to 180 degree(s)C and this limits the catalyst activity, and hence their sensitivity and response time. In addition, the fabrication of an integrated, resistive heater poses interesting problems; thus whilst polysilicon heaters are CMOS compatible, they tend to suffer from non-linearity, poor reproducibility and stability; whereas platinum resistive heaters are incompatible with a CMOS process and thus difficult and expensive to manufacture. Here we propose the use of SOI technology leading to a new generation of high-temperature, silicon smart gas sensors (patent pending). Numerical simulations of an n-channel MOSFET structure on a thin SOI membrane have been performed in non- isothermal conditions using a MEDICI simulator. Our results demonstrate that SOI-based devices can operate at temperatures of up to 350 degree(s)C without causing a problem for neighboring CMOS I.C. circuitry. The power consumption of our SOI-based designs may be as low as ca. 10 mW at 300 degree(s)C and so compares favorably with previously reported values for non-SOI based silicon micromachined gas sensors. In conclusion, SOI technology may be used to fabricate novel high-temperature, micropower resistive and catalytic-gate MOSFET gas/odor sensors. These devices can be fabricated in a standard SOI CMOS process at low unit cost and should offer an excellent degree of reproducibility. Applications envisaged are in air quality sensors for the automotive industry and odor sensors for electronic noses.
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